Heart rate and rhythm irregularities can sometimes have catastrophic consequences. A heart rate that is too fast is referred to as tachycardia, while a heart rate that is too slow is referred to as bradycardia. A rhythm disturbance or arrhythmia is a condition in which the chambers of the heart do not contract in the appropriate sequence or with the appropriate timing. For example, in a type of arrhythmia known as atrial fibrillation, the upper chambers of the heart tend to quiver or contract in a disorganized manner. The resulting turbulence tends to form blood clots, which can travel downstream to a location where they causes a blockage (e.g., a stroke).
Many types of heart rhythm irregularity, including atrial fibrillation, cause no pain or discomfort. Although the causes of such arrhythmias tend to be treatable, and the likelihood of inappropriate clotting thereby reduced significantly, it is necessary first to know that the condition exists. Because episodes of arrhythmia tend to be painless and transient, the need for treatment might not be identified by a health care professional unless the episode occurs, perhaps coincidentally, while the patient is being examined.
Portable heart rate monitors, capable of detecting rate and rhythm irregularities, are well known. Some rely on simple two-lead electrocardiographic analysis, a good example being the devices commonly found in health clubs that can show the user's heart rate when the user touches the electrodes on the two hand grips of, for instance, an exercise bicycle. Another common technique can detect rate and rhythm irregularities optically, via a process known as photoplethysmography, which is the method underlying pulse oximeters. However, these conventional portable heart monitors require the user to initiate the monitoring.